Three-dimensional magnetic memory with multi-layer data storage layers

ABSTRACT

Magnetic memories and methods are disclosed. A magnetic memory as described herein includes a plurality of stacked data storage layers to form a three-dimensional magnetic memory. The data storage layers are each formed from a multi-layer structure. At ambient temperatures, the multi-layer structures exhibit an antiparallel coupling state with a near zero net magnetic moment. At higher transition temperatures, the multi-layer structures transition from the antiparallel coupling state to a parallel coupling state with a net magnetic moment. At yet higher temperatures, the multi-layer structure transitions from the antiparallel coupling state to a receiving state where the coercivity of the multi-layer structures drops below a particular level so that magnetic fields from write elements or neighboring data storage layers may imprint data into the data storage layer.

RELATED APPLICATIONS

This patent application relates to a U.S. patent application having theSer. No. 11/615,618 that was filed on Dec. 22, 2006, which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to the field of memories and, in particular, toa three-dimensional magnetic memory comprised of a stack of data storagelayers. More particularly, the data storage layers of thethree-dimensional magnetic memory are formed from multi-layerstructures.

2. Statement of the Problem

Solid-state memory is a nonvolatile storage medium that uses no movingparts. Some examples of solid-state memory are flash memory and MRAM(magnetoresistive random access memory). Solid-state memories provideadvantages over conventional disk drives in that data transfers to andfrom solid-state memories take place at a much higher speed than ispossible with electromechanical disk drives. Solid-state memories mayalso have a longer operating life and may be more durable due to thelack of moving parts. One problem with traditional solid-state memoriesis that storage capacity is much less than can be achieved withelectromechanical disk drives. For instance, a common flash memory maystore up to approximately 1 gigabyte (GB), whereas a common hard drivemay store up to 100 GB or more. The cost per megabyte is higher forsolid-state memories than for electromechanical disk drives.

Solid-state memories have a size that is determined by a minimum featuresize (F). One problem with solid-state magnetic memories (as opposed toflash memory) is the cell density of the memory. A typical solid-statemagnetic memory has a cell size that is large compared to flash memoriesdue to the nature of magnetic fields from current lines extending over atypical 4 F distance range. For instance, an MRAM may have a cell sizeof 32 F² while a flash memory may have a cell size of 4 F². The largercell size of solid-state magnetic memories unfortunately relates to areduced cell density.

It may thus be desirable to design solid-state magnetic memories thathave reduced cell size.

SUMMARY OF THE SOLUTION

The invention solves the above and other related problems with athree-dimensional solid-state magnetic memory. The three-dimensionalmagnetic memory includes a plurality of stacked data storage layerswhere each data storage layer is adapted to store bits of data. The bitsmay be transferred between the data storage layers as desired. By usingstacked data storage layers to form a three-dimensional magnetic memory,the net cell size is advantageously reduced which allows for increasedcell density. For instance, assume a two-dimensional magnetic memoryinitially has a cell size of 16 F². If the magnetic memory isimplemented with four stacked data storage layers as described hereininstead of one data storage layer, then the effective cell size can bereduced to 4 F². If the magnetic memory is implemented with sixteenstacked data storage layers as described herein instead of one datastorage layer, then the effective cell size can be reduced to 1 F². Thethree-dimensional magnetic memory as described herein advantageouslycompetes with flash memories and disk drives in terms of cell density(or bit density).

One embodiment of the invention is a magnetic memory having stacked datastorage layers. The magnetic memory includes a first storage stackincluding a first data storage layer defining a first plane. The stackis a sequence of thin films, deposited one on top of another, and formsa fundamental building block of the magnetic memory described herein.The magnetic memory further includes a plurality of secondary storagestacks, where the secondary storage stacks include second data storagelayers defining secondary planes that are parallel to the first plane.The first plane and the secondary planes are in the X-Y direction, andthe data storage layers are thus stacked in the Z direction.

The first data storage layer and the secondary data storage layers areeach formed from a magnetic multi-layer structure having an antiparallelcoupling between the constituent layers at ambient temperatures. Forexample, a data storage layer may include a first ferromagnetic layer,an antiparallel (AP) coupling layer, a second ferromagnetic layer, and athird ferromagnetic layer. The first ferromagnetic layer and the secondferromagnetic layer/third ferromagnetic layer are antiparallel coupledacross the AP coupling layer at ambient temperatures, also referred toas an antiparallel temperature (T_(AP)). The thicknesses andmagnetizations of the constituent layers can be tuned such that there isa zero (or near zero) net magnetic moment in the data storage layer atambient temperature and low fields. By having the data storage layers inan antiparallel coupling state at T_(AP), the data storage layers arenot written to by magnetic stray fields of neighboring data storagelayers. Similarly, the data storage layers have a net magnetic momentnear zero, so they do not write to neighboring data storage layers. Thedata storage layers may thus be fabricated close to one another creatinga higher density magnetic memory.

The first data storage layer and the secondary data storage layers arealso each formed to transition from an antiparallel coupling state to aparallel coupling state at higher temperatures, which are referred to asa transition temperature (T_(T)). To accomplish this in one embodiment,the first ferromagnetic layer and the third ferromagnetic layer of adata storage layer have a Curie temperature that is higher than theCurie temperature of the second ferromagnetic layer. Thus, when the datastorage layer is heated above the Curie temperature of the secondferromagnetic layer, the first ferromagnetic layer and the thirdferromagnetic layer are no longer antiparallel coupled across the APcoupling layer and the second ferromagnetic layer. The firstferromagnetic layer and the third ferromagnetic layer transition toparallel coupling having a net magnetic moment. The net magnetic momentof the data storage layer may be used to write to other neighboring datastorage layers. It may be noted that there is one naturally occurringclass of materials, namely chemically ordered alloys of iron and rhodium(FeRh), that shows a very similar behavior. However, compared to thesolution proposed here these materials require prohibitively highprocessing temperatures to achieve the chemical ordering.

The first data storage layer and the secondary data storage layers arealso each formed to transition from an antiparallel coupling state to areceiving state at even higher temperatures, which is referred to as areceiving temperature (T_(R)). The receiving temperature is close to theCurie temperatures of the first ferromagnetic layer and the thirdferromagnetic layer of a data storage layer. When heated to thereceiving temperature, the coercivity of the first ferromagnetic layeror the third ferromagnetic layer drops below the strength of externalmagnetic fields, such as from write elements or a neighboring datastorage layer. Thus, the external magnetic fields imprint a plurality ofmagnetic domains in the first ferromagnetic layer or the thirdferromagnetic layer. The magnetic domains represent a plurality of bitsbeing stored in the data storage layer. With the magnetic domainsimprinted in the first ferromagnetic layer or the third ferromagneticlayer, the data storage layer may be cooled back to the antiparalleltemperature (T_(AP)), which transitions the data storage layer back toan antiparallel coupling state.

The invention may include other exemplary embodiments described below.

DESCRIPTION OF THE DRAWINGS

The same reference number represents the same element or same type ofelement on all drawings.

FIG. 1A is an isometric view of a magnetic memory in an exemplaryembodiment of the invention.

FIG. 1B is a cross-sectional view of a magnetic memory in an exemplaryembodiment of the invention.

FIG. 2 is a cross-sectional view of a data storage layer in an exemplaryembodiment of the invention.

FIG. 3 is a graph illustrating the magnetic moment of a data storagelayer at ambient temperatures (25 degrees Celsius) in an exemplaryembodiment of the invention.

FIG. 4 is a graph illustrating the magnetic moment of a data storagelayer at a transition temperature (125 degrees Celsius) in an exemplaryembodiment of the invention.

FIG. 5 is a graph illustrating the magnetic moment of a data storagelayer as a function of temperature in an exemplary embodiment of theinvention.

FIG. 6 is another cross-sectional view of a data storage layer in anexemplary embodiment of the invention.

FIG. 7 is a top view of read elements in a magnetic memory in anexemplary embodiment of the invention.

FIG. 8 is a top view of write elements in a magnetic memory in anexemplary embodiment of the invention.

FIGS. 9A-9B are flow charts illustrating a method of writing bits to amagnetic memory in an exemplary embodiment of the invention.

FIG. 10 is an isometric view of a portion of a data storage layerillustrating bits written to the data storage layer in an exemplaryembodiment of the invention.

FIG. 11 illustrates a magnetic memory with bits written into a firstdata storage layer in an exemplary embodiment of the invention.

FIG. 12 illustrates a magnetic memory with the bits copied from a firstdata storage layer to a second data storage layer in an exemplaryembodiment of the invention.

FIG. 13 illustrates a magnetic memory with the bits copied from a seconddata storage layer to a third data storage layer in an exemplaryembodiment of the invention.

FIGS. 14A and 14B are flow charts illustrating a method of reading bitsfrom a magnetic memory in an exemplary embodiment of the invention.

FIG. 15 illustrates a magnetic memory with bits stored in a third datastorage layer in an exemplary embodiment of the invention.

FIG. 16 illustrates a magnetic memory with the bits copied from a thirddata storage layer to a second data storage layer and from the seconddata storage layer to a first data storage layer in an exemplaryembodiment of the invention.

FIG. 17 illustrates a magnetic memory that includes an overflow storagesystem in an exemplary embodiment of the invention.

FIG. 18 illustrates a heating layer comprised of intersecting conductorsin an exemplary embodiment of the invention.

FIG. 19 illustrates a data storage layer as patterned in an exemplaryembodiment of the invention.

FIG. 20 illustrates another data storage layer as patterned in anexemplary embodiment of the invention.

FIG. 21 illustrates another data storage layer as patterned in anotherexemplary embodiment of the invention.

FIG. 22 is a flow chart illustrating a method of fabricating a magneticmemory in an exemplary embodiment of the invention.

FIG. 23 is a flow chart illustrating a method of fabricating a storagestack in an exemplary embodiment of the invention.

FIG. 24 is a flow chart illustrating a method of fabricating a datastorage layer in an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-24 and the following description depict specific exemplaryembodiments of the invention to teach those skilled in the art how tomake and use the embodiments. For the purpose of teaching inventiveprinciples, some conventional aspects of the embodiments have beensimplified or omitted. Those skilled in the art will appreciatevariations from these embodiments that fall within the scope of theinvention. Those skilled in the art will appreciate that the featuresdescribed below can be combined in various ways to form multiplevariations of the invention. As a result, the invention is not limitedto the specific embodiments described below, but only by the claims andtheir equivalents.

FIG. 1A is an isometric view of magnetic memory 100 in an exemplaryembodiment of the invention. The view in FIG. 1A only shows a portion ofmagnetic memory 100, as an actual magnetic memory may extend further inthe X, Y, or Z direction. Magnetic memory 100 includes a main column 101of layers comprising a layer of read elements 102, a layer of writeelements 104, a first storage stack 110, a second storage stack 120, anda third storage stack 130. Although one main column 101 of layers isshown in FIG. 1A, magnetic memory 100 may include a plurality of maincolumns as shown in FIG. 1A. For instance, if the main column 101 shownin FIG. 1A provides 4 Mbits of storage (such as 2K in the X-directionand 2K in the Y direction), then magnetic memory 100 may include aplurality of main columns 101 as shown in FIG. 1A to provide 16 Mbits,32 Mbits, 64 Mbits, etc.

The layer of read elements 102 and the layer of write elements 104 areproximate to storage stack 110, storage stack 110 is proximate tostorage stack 120, and storage stack 120 is proximate to storage stack110 and storage stack 130. Being proximate means that one stack isadjacent to or adjoining another stack. There may be more or lessstorage stacks in magnetic memory 100 that are not illustrated in thisembodiment. For instance, magnetic memory 100 may include a fourthstorage stack, a fifth storage stack, etc.

A storage stack comprises any subset of layers adapted to store bits ofdata. Storage layer 110 includes data storage layer 112, an insulatinglayer 114, and a heating layer 116. Data storage layer 112 is adapted tostore bits of data in form of magnetic domains. Insulating layer 114 isadapted to insulate heating of data storage layer 112 from other datastorage layers. Heating layer 116 is adapted to heat data storage layer112. Storage stack 110 may include additional layers other than shown inFIG. 1A. Alternatively, storage stack 110 may not include all of thelayers illustrated in FIG. 1A. For instance, storage stack 110 may notinclude heating layer 116 in some embodiments, as current may be applieddirectly to data storage layer 112 in order to heat this layer.

Storage stack 120 may have a similar configuration as storage stack 110having a data storage layer 122, an insulating layer 124, and a heatinglayer 126. Storage stack 130 may have a similar configuration as storagestack 110 with a data storage layer 132, an insulating layer 134, and aheating layer 136.

Data storage layer 112 of storage stack 110 defines a first plane in theX-Y direction. Data storage layer 122 of storage stack 120 defines asecond plane in the X-Y direction. Data storage layer 132 of storagestack 130 defines a third plane in the X-Y direction. As is evident inFIG. 1A, the first plane, the second plane, and the third plane of thedata storage layers are parallel to one another.

FIG. 1B is a cross-sectional view of magnetic memory 100 in an exemplaryembodiment of the invention. As illustrated in FIG. 1B, magnetic memory100 also includes a control system 150 that may be comprised of aplurality of transistors and/or other processing elements. Controlsystem 150 is adapted to control how data is written to the storagestacks 110, 120, and 130, how data is moved between the storage stacks110, 120, and 130 in the Z direction, and how data is read from thestorage stacks 110, 120, and 130.

According to embodiments described herein, data storage layers 112, 122,and 132 are formed from a multi-layer structure. Data storage layers112, 122, and 132 may thus be also referred to as data storagestructures. FIG. 2 is a cross-sectional view of data storage layer 112in an exemplary embodiment of the invention. Data storage layers 122 and132, and other data storage layers in magnetic memory 100, may be formedfrom a similar multi-layer structure as shown in FIG. 2.

In FIG. 2, data storage layer 112 includes a first ferromagnetic layer202, an antiparallel (AP) coupling layer 204, a second ferromagneticlayer 206, and a third ferromagnetic layer 208. Data storage layer 112has the characteristic of having antiparallel (or antiferromagnetic)coupling at certain temperatures, such as ambient temperatures. Whendata storage layer 112 exhibits antiparallel coupling, data storagelayer 112 is considered to be in an antiparallel coupling state. Thetemperature where data storage layers have the characteristic of havingantiparallel coupling is referred to herein as an antiparalleltemperature (T_(AP)). To have antiparallel coupling, ferromagnetic layer202 is antiparallel coupled to the combination of ferromagnetic layers206 and 208 across AP coupling layer 204 at T_(AP). As a result, the netmagnetic moment of data storage layer 112 is zero or near zero atT_(AP). FIG. 3 is a graph illustrating the magnetic moment of datastorage layer 112 at T_(AP) (25 degrees Celsius) in an exemplaryembodiment of the invention. As is illustrated in FIG. 3, data storagelayer 112 has near zero magnetic moment in the absence of a strongmagnetic field. This is due to the antiparallel coupling in data storagelayer 112.

Data storage layer 112 also has the characteristic of transitioning toparallel (or ferromagnetic) coupling at higher temperatures. When datastorage layer 112 is heated to a transition temperature (T_(T)),ferromagnetic layer 202 is no longer antiparallel coupled toferromagnetic layers 206 and 208 across AP coupling layer 204 andinstead becomes coupled parallel to ferromagnetic layer 208. When datastorage layer 112 exhibits parallel coupling, data storage layer 112 isconsidered to be in a parallel coupling state. When in the parallelcoupling state, data storage layer 112 has a net remnant magneticmoment. The transition temperature T_(T) is a temperature close to theCurie temperature of ferromagnetic layer 206 where ferromagnetic layer206 becomes paramagnetic and ferromagnetic layer 202 and 208 areparallel coupled by dipolar fields.

FIG. 4 is a graph illustrating the magnetic moment of data storage layer112 at T_(T) (125 degrees Celsius) in an exemplary embodiment of theinvention. As is illustrated in FIG. 4, data storage layer 112 has a netmagnetic moment at a zero external magnetic field. This is due to theparallel coupling in data storage layer 112.

To create the transition from antiparallel coupling to parallel couplingin data storage layer 112, ferromagnetic layer 202 and ferromagneticlayer 208 are formed from materials having a higher Curie temperaturethan ferromagnetic layer 206. For instance, ferromagnetic layer 206 mayhave a Curie temperature of about 100 degrees Celsius whileferromagnetic layers 202 and 208 may have a Curie temperature of about200 degrees Celsius. At ambient temperatures (around 25 degreesCelsius), ferromagnetic layer 202 is antiparallel coupled toferromagnetic layers 206 and 208 across AP coupling layer 204. Datastorage layer 112 thus has a zero net magnetic moment at thistemperature. FIG. 5 is a graph illustrating the magnetic moment of datastorage layer 112 as a function of temperature in an exemplaryembodiment of the invention. As is evident in FIG. 5, the net magneticmoment of data storage layer 112 at T_(AP) (around 25 degrees Celsius)is about zero.

When data storage layer 112 is heated from an antiparallel temperature(T_(AP)) to above the Curie temperature of ferromagnetic layer 206(about 100 degrees Celsius), the magnetic moment of ferromagnetic layer206 vanishes and there is no longer exchange coupling betweenferromagnetic layer 202 and ferromagnetic layer 208 (see FIG. 2). Theeffective coupling between ferromagnetic layer 202 and ferromagneticlayer 208 aligns their magnetic moments in parallel. The net magneticmoment of data storage layer 112 is thus the sum of the magnetic momentsof ferromagnetic layer 202 and ferromagnetic layer 208 at the transitiontemperature (T_(T)). In FIG. 5, the graph shows that the net magneticmoment of data storage layer 112 transitions from about zero to about330 emu/cm³ when data storage layer 112 is heated above about 100degrees Celsius (which may be considered a parallel temperature in thisembodiment).

If data storage layer 112 is cooled below the Curie temperature offerromagnetic layer 206 to T_(AP), then the magnetic moment offerromagnetic layer 206 appears again and there is exchange couplingbetween ferromagnetic layer 202 and the combination of ferromagneticlayer 206 and ferromagnetic layer 208 (see FIG. 2). The magnetic momentsof ferromagnetic layer 202 and the combination of ferromagnetic layer206 and ferromagnetic layer 208 return to an antiparallel couplingstate. Also, the net magnetic moment of data storage layer 212 returnsto zero or near zero (see FIG. 5).

Another characteristic of data storage layer 112 is that it may not bewritable at the transition temperature (T_(T)). Near the transitiontemperature, the coercivity of data storage layer 112 is still high, soit is not influenced by external magnetic fields. To make data storagelayer 112 writable, it is heated above the transition temperature tohigher temperatures that are close to the Curie temperatures offerromagnetic layer 202 and ferromagnetic layer 208, which is referredto as the receiving temperature (T_(R)) (T_(AP)<T_(T)<T_(R)). At thereceiving temperature, the coercivity of data storage layer 112 dropsbelow a write threshold where a data storage layer is writable. Thewrite threshold is less than the magnitude of external magnetic fieldsthat are attempting to write to the data storage layer. When at thereceiving temperature, data storage layer 112 is considered to be in areceiving state.

To achieve this characteristic, one of ferromagnetic layer 202 orferromagnetic layer 208 has a higher coercivity (Hc) than the other(i.e., one layer is harder than the other). When data storage layer 112is heated to the receiving temperature (T_(R)), the coercivity of thesofter one of ferromagnetic layer 202 or ferromagnetic layer 208 dropsbelow the level of external magnetic fields. Thus, the external magneticfields imprint a plurality of magnetic domains in ferromagnetic layer202 or ferromagnetic layer 208. The magnetic domains represent aplurality of bits being stored in the data storage layer.

FIG. 6 is another cross-sectional view of data storage layer 112 in anexemplary embodiment of the invention. FIG. 6 illustrates a detailedstructural composition of one exemplary embodiment of data storage layer112, and data storage layer 112 is not limited to this structuralcomposition. In this embodiment, ferromagnetic layer 202, AP couplinglayer 204, ferromagnetic layer 206, and ferromagnetic layer 208 eachcomprise multi-layer structures.

In particular, ferromagnetic layer 202 comprises a multi-layer structurehaving alternating Co layers 602 and Pd (or Pt) layers 603 (indicated byhatched layers). AP coupling layer 204 comprises a multi-layer structurehaving a Ru (or Ir) layer 604 and a Co layer 605. The thickness of Rulayer 604 may be about 6 Å. The thickness of Co layer 605 may be about 5Å. Ferromagnetic layer 206 comprises a multi-layer structure havingalternating CoNi layers 606 and Pd (or Pt) layers 607. Ferromagneticlayer 208 comprises a multi-layer structure having alternating Co layers608 and Pd layers 609.

The multi-layer structure of CoNi layers 606 and Pd layers 607 has alower Curie temperature than the multi-layer structure of Co layers 602and Pd layers 603 and the multi-layer structure of Co layers 608 and Pdlayers 609. Thus, this embodiment of data storage layer 112 has thecharacteristics of having antiparallel coupling at antiparalleltemperatures, and having parallel coupling at temperatures above theCurie temperature of the multi-layer structure of CoNi layers 606 and Pdlayers 607.

The following FIGS further illustrate the structure of magnetic memory100 (see FIG. 1) and how data is written to and read from magneticmemory 100. FIG. 7 is a top view of read elements 102 in an exemplaryembodiment of the invention. Read elements 102 are in an array in theX-Y direction. Read elements 102 are spaced according to a desired bitdensity in the data storage layers 112, 122, and 132. Read elements 102comprise any elements adapted to sense magnetic fields from domains thatrepresent bits stored on data storage layer 112. For example, readelements 102 may comprise Hall Effect elements, spin valve elements, ortunnel valve elements.

FIG. 8 is a top view of write elements 104 in an exemplary embodiment ofthe invention. Write elements 104 are formed from a cross-point array ofcurrent loops. An individual write element 104 is indicated by thedotted circle in FIG. 8. Current loops 802 (which are formed fromconductive material) travel in the X direction, and current loops 804travel in the Y direction. The intersection points of the current loopscorrespond with the locations of the read elements 102 which areillustrated as dotted boxes. Current loops 802 and 804 each generate amagnetic field of magnitude X. In locations where the current loops donot intersect, the magnetic field has a magnitude of X. In locationswhere the current loops intersect, the magnetic fields from both currentloops are additive to generate a magnetic field having a magnitude of2×. The 2× magnetic field is used to write bits to data storage layer112 of FIG. 1.

According to features and aspects herein, magnetic memory 100 (seeFIG. 1) is adapted to provide storage of bits in the data storage layers112, 122, and 132 (and possibly other data storage layers not shown). Tostore the bits in magnetic memory 100, each of the data storage layers112, 122, and 132 are able to store bits in the X-Y direction. Magneticmemory 100 is also able to transfer bits in the Z direction in FIG. 1between the data storage layers 112, 122, and 132. As previously stated,data storage layers 112, 122, and 132 each include anantiferromagnetically (AF) coupled sub-layer structure, which exhibits anet magnetic moment of about zero at ambient temperatures.

FIGS. 9A and 9B are flow charts illustrating a method 900 of writingbits to magnetic memory 100 in an exemplary embodiment of the invention.FIG. 9A illustrates the initial writing of bits to data storage layer112 by write elements 104. In step 902, control system 150 heats datastorage layer 112 to receiving temperature (T_(R)) where the datastorage layer 112 transitions from the antiparallel coupling state tothe receiving state. When in the receiving state, data storage layer 112is writable, such as by write elements 104.

In step 904, write elements 104 apply magnetic fields to data storagelayer 112 to create or imprint a plurality of magnetic domains in datastorage layer 112. A magnetic domain comprises a region of magnetizationsurrounded by regions of a different magnetization (or backgroundmagnetization). The magnetic domains represent a plurality of bits ofdata that is written into data storage layer 112. Magnetic domains mayalso be referred to herein as regions of magnetization or magneticimprints.

In step 906, control system 150 cools data storage layer 112. Controlsystem 150 cool data storage layer 112 down to the antiparalleltemperature (T_(AP)) so that data storage layer 112 transitions from thereceiving state back to the antiparallel coupling state. When in theantiparallel coupling state, data storage layer 112 cannot be written toby any neighboring data storage layers 122 and 132. Also, data storagelayer 112 does not emit strong magnetic stray fields that may influencethe magnetization of neighboring data storage layers 122 and 132.

FIG. 10 is an isometric view of a portion of data storage layer 112illustrating bits written to data storage layer 112. Data storage layer112 has a background magnetization, such as a magnetizationperpendicular to the plane pointing downward in FIG. 10. Bits arewritten to data storage layer 112 in the form of magnetic domains 1002.The magnetic domains 1002 are formed by changing the magnetizationlocally to a polarity opposite than the primary magnetization of datastorage layer 112. The magnetization of magnetic domains 1002 isillustrated by arrows in FIG. 10. The existence of a magnetic domain1002 magnetized opposite to the background magnetization indicates onebinary value of a bit, such as a “1”. The absence of anoppositely-magnetized domain 1002 in a particular region in data storagelayer 112 indicates another binary value of a bit, such as a “0”. Theabsence of a magnetic domain 1002 in FIG. 10 is illustrated as a dottedcircle.

FIG. 11 illustrates magnetic memory 100 with bits written into datastorage layer 112 according to step 904 of FIG. 9A. A magnetic domainhas been imprinted into data storage layer 112 by the rightmost writeelement 104 and the middle write element 104. The magnetic domains areindicated by a single arrow pointing upward in a dotted box representinga region proximate to the rightmost write element 104 and a regionproximate to the middle write element 104. The background magnetizationwith no opposite domain has been imprinted into data storage layer 112proximate to the leftmost write element 104. The absence of an oppositemagnetic domain is indicated by a dotted box representing a regionproximate to the leftmost write element 104 that does not include anarrow.

With the bits written into data storage layer 112 in FIG. 11, controlsystem 150 may transfer the bits up main column 101 of magnetic memory100 to data storage layer 122 according to the method described in FIG.9B. In step 908, control system 150 heats data storage layer 122 to thereceiving temperature (T_(R)). By heating to the receiving temperature,data storage layer 122 transitions from the antiparallel coupling stateto the receiving state (i.e., the coercivity of data storage layer 112drops below a level of external magnetic fields being emitted from atransmitting layer). Data storage layer 122 may be considered the“receiving” data storage layer as it will be receiving bits from datastorage layer 112.

In step 910, control system 150 heats data storage layer 112 (if alreadycooled) to the transition temperature (T_(T)) where the data storagelayer 112 transitions from the antiparallel coupling state to theparallel coupling state. When data storage layer 112 is in the parallelcoupling state, the magnetic domains representing the stored data areemitted as magnetic stray fields. Data storage layer 112 may beconsidered the “transmitting” data storage layer. The external strayfields imprint the magnetic domains from data storage layer 112 intodata storage layer 122. By imprinting the magnetic domains from datastorage layer 112 to data storage layer 122, the bits stored in datastorage layer 112 are copied to data storage layer 122 in the Zdirection (upward in FIG. 11). FIG. 12 illustrates magnetic memory 100with the bits copied from data storage layer 112 to data storage layer122. The absence of an isolated magnetic domain is also illustrated inFIG. 12 by a dotted box

In step 912 of FIG. 9B, control system 150 cools data storage layer 122.Data storage layer 122 cools from T_(R) to T_(AP) where data storagelayer 122 transitions from the receiving state to the antiparallelcoupling state. Control system 150 then cools data storage layer 112 toT_(AP) in order to transition data storage layer 112 from the parallelcoupling state back to an antiparallel coupling state in step 914.Although heat is used in this embodiment to imprint the magnetic domainsfrom data storage layer 112 to data storage layer 122, other methods ormeans may be used to facilitate the transfer of the magnetic domains.

With the bits written into data storage layer 122 in FIG. 12, controlsystem 150 may transfer the bits up main column 101 again. Controlsystem 150 may repeat steps 908-914 as shown in FIG. 9B to transfer thebits from data storage layer 122 (the “transmitting” data storage layer)to data storage layer 132 (the “receiving” data storage layer). FIG. 13illustrates magnetic memory 100 with the bits copied from data storagelayer 122 to data storage layer 132.

After copying bits from one data storage layer to another, controlsystem 150 may erase the bits from the transmitting data storage layer.For instance, to erase bits from data storage layer 112, control system150 may heat data storage layer 112 above its Curie temperature. Asillustrated in FIG. 2, if control system 150 heats data storage layer112 to the Curie temperature of ferromagnetic layer 202 andferromagnetic layer 208, then data storage layer 112 returns to itsprimary or background magnetization after it is cooled. Control system150 may heat and cool data storage layer 112 in the presence of a biasfield in order to return data storage layer 112 to its primary orbackground magnetization. The bits are thus erased from data storagelayer 112.

In FIG. 13, the bits originally written to data storage layer 112 havebeen copied to data storage layer 122 and data storage layer 132. Thebits may be stored in data storage layer 132, or may be transferred upthe stack of magnetic memory 100 (although additional storage stackshave not been illustrated in FIG. 13). With the bits stored in datastorage layer 132, control system 150 may erase the bit pattern storedin data storage layer 112 and write elements 104 may write another bitpattern into data storage layer 112. Control system 150 may erase thebit pattern stored in data storage layer 122 and transfer the new bitpattern from data storage layer 112 to data storage layer 122. With onebit pattern stored in data storage layer 132 and another bit patternstored in data storage layer 122, control system 150 may erase the bitpattern stored in data storage layer 112 and write elements 104 maywrite yet another bit pattern into data storage layer 112 if desired.

At some point, the bits stored in data storage layers 112, 122, or 132may be read from magnetic memory 100. FIGS. 14A and 14B are flow chartsillustrating a method 1400 of reading bits from magnetic memory 100 inan exemplary embodiment of the invention. To read bits from a particulardata storage layer, the bits may need to be moved down main column 101(see FIG. 13) until the bits reach data storage layer 112 (which isproximate to read elements 102). For example, assume that bits arestored in data storage layer 132 which are to be read. FIG. 15illustrates magnetic memory 100 with the bits stored in data storagelayer 132 in an exemplary embodiment. To read the bits in data storagelayer 132, the bits need to be transferred down main column 101 to datastorage layer 112 because data storage layer 112 is proximate to readelements 102. If other bit patterns are stored in data storage layer 112or data storage layer 122, these bits patterns are read and temporarilyoffloaded to an overflow storage system, which is described in FIG. 17.

In step 1402 of FIG. 14A, control system 150 heats data storage layer122 to T_(R). By heating to the receiving temperature (T_(R)), datastorage layer 122 transitions from the antiparallel coupling state tothe receiving state (i.e., the coercivity of data storage layer 112drops below a level of external magnetic fields being emitted from atransmitting layer). Data storage layer 122 may be considered the“receiving” data storage layer as it will be receiving bits from datastorage layer 132.

In step 1404, control system 150 heats data storage layer 132 (ifalready cooled) to T_(P) where the data storage layer 132 transitionsfrom the antiparallel coupling state to the parallel coupling state.When data storage layer 132 is in a parallel coupling state, themagnetic domains representing the stored data are emitted as magneticstray fields. Data storage layer 132 may be considered the“transmitting” data storage layer. The external stray fields imprint themagnetic domains from data storage layer 132 into data storage layer122. By imprinting the magnetic domains from data storage layer 132 todata storage layer 122, the bits stored in data storage layer 132 arecopied to data storage layer 122 in the Z direction (downward in FIG.15).

In step 1406, control system 150 cools data storage layer 122. Datastorage layer 122 cools from T_(R) to T_(AP) where data storage layer122 transitions from the receiving state to the antiparallel couplingstate. Control system 150 then cools data storage layer 112 to T_(AP) inorder to transition data storage layer 112 from the parallel couplingstate back to the antiparallel coupling state in step 1408 (see FIG.14A). Although heat is used in this embodiment to imprint the magneticdomains from data storage layer 132 to data storage layer 122, othermethods or means may be used to facilitate the transfer of the magneticdomains.

The bits of data to be read are now in data storage layer 122 and theyneed to be transferred down main column 101 into data storage layer 112to be read. Thus, control system 150 repeats steps 1402-1408 of FIG. 14Ato copy the bits from data storage layer 122 (the transmitting datastorage layer) to data storage layer 112 (the receiving data storagelayer). FIG. 16 illustrates magnetic memory 100 with the bits copiedfrom data storage layer 132 to data storage layer 122 and from datastorage layer 122 to data storage layer 112.

After copying bits from one data storage layer to another, controlsystem 150 may erase the bits from the transmitting data storage layer.Control system 150 may erase the bits in a similar manner as previouslydescribed.

With the bits transferred to data storage layer 112 that is proximate toread elements 102, the bits are in a position to be read by readelements 102. In step 1410 of FIG. 14B, control system 150 heats datastorage layer 112 (if already cooled) to T_(T) where the data storagelayer 112 transitions from the antiparallel coupling state to theparallel coupling state. When data storage layer 112 is in a parallelcoupling state, the magnetic domains representing the stored data areemitted as magnetic stray fields.

In step 1412, read elements 102 sense magnetic fields from the magneticdomains in data storage layer 112 to read the bits from data storagelayer 112. If read elements 102 are spin valves, for instance, theresistance of the spin valve will depend on the direction and magnitudeof the field emanating from data storage layer 112. For example,upward-pointing magnetic fields from a magnetic domain will result inone value of resistance, while a downwardly-pointing magnetic field willresult in a second resistance. An isolated magnetic domain thus resultsin one resistance, while the background magnetization, or no isolateddomain, results in a second resistance.

In step 1414, control system 150 may then cool data storage layer 112from T_(T) to T_(AP) to transition data storage layer 112 from theparallel coupling state back to the antiparallel coupling state.

During the read process described above, data may need to be moved fromdata storage layer 112, data storage layer 122, etc, in order to movethe data to be read down main column 101. To temporarily move the data,an overflow storage system may be used. FIG. 17 illustrates magneticmemory 100 that includes an overflow storage system 1702. Overflowstorage system 1702 may comprise any desired memory adapted to store thebits read from data storage layer 112. Overflow storage system 1702 mayinclude one or more storage stacks much like storage stacks 110, 120,and 130. Overflow storage system 1702 may serve a single column ofmagnetic memory 100 shown in FIG. 17, or may serve multiple columns ofmagnetic memory 100 which are not shown. As illustrated in FIG. 17, bothdata storage layer 122 and data storage layer 132 are storing bits. Datastorage layer 122 stores a first bit pattern and data storage layer 132stores a second bit pattern. If a request is received in magnetic memory100 for the bits stored in data storage layer 132, then control system150 operates as described in FIG. 14A to move the first bit pattern indata storage layer 122 to overflow storage system 1702. Control system150 also operates as described in FIGS. 14A and 14B to move the secondbit pattern in data storage layer 132 to data storage layer 112 and toread the bits from data storage layer 112. After the second bit patternpreviously stored in data storage layer 132 has been read, controlsystem 150 may write the first bit pattern being stored in overflowstorage system 1702 back onto data storage layer 122 or another datastorage layer in magnetic memory 100.

As illustrated in FIG. 1, storage stacks 110, 120, and 130 may eachinclude a heating layer 116, 126, and 136. FIG. 18 illustrates a heatinglayer 116 comprised of intersecting conductors in an exemplaryembodiment of the invention. FIG. 18 is a top view of a heating layer116 comprising intersecting conductors. The horizontal conductors 1802and the vertical conductors 1804 in FIG. 18 intersect at a plurality ofpoints. The intersection points of the conductors 1802, 1804 correspondwith the locations of the magnetic domains in data storage layer 112(i.e., the locations where bits are stored). In this embodiment,conductors 1802, 1804 are not uniform in width. The widths of conductors1802, 1804 are narrower at the intersection points (i.e., the bitlocations) as compared to the widths of conductors 1802, 1804 betweenthe intersection points. With conductors 1802, 1804 narrower at theintersections points, the power dissipation is higher which results inhigher temperatures at the intersections points. With conductors 1802,1804 wider between the intersections points, the power dissipation islower which results in lower temperatures between the intersectionspoints. One advantage of this configuration is that less power isconsumed as higher temperatures are only provided at the intersectionspoints. Another advantage is that higher thermal gradients may beacquired in data storage layer 112 along the lengths on the conductors1802, 1804 because the regions in data storage layer 112 between the bitlocations remain cooler. Another advantage is faster cooling time as asmaller volume of data storage layer 112 is heated and thus cooled.Another advantage is that the resistance of the wires can be lower asthe average width of the conductors 1802, 1804 is larger.

In regards to FIG. 10, magnetic domains 1002 may grow larger when beingtransferred from one data storage layer to another. The magnetic fieldsfrom the magnetic domains 1002 are not perfectly perpendicular and tendto diverge at the domain walls. Due to this occurrence, the magneticdomains may grow in size when being transferred to successive datastorage layers which can affect the overall density of the magneticmemory 100 (see FIG. 1). According to features and aspects herein, thedata storage layers in magnetic memory 100 may be patterned in oneembodiment to control the size of the magnetic domains.

FIG. 19 illustrates data storage layer 112 as patterned in an exemplaryembodiment of the invention. Data storage layer 112 is patterned intostrips in this embodiment. The locations of the strips correspond withthe magnetic domains in data storage layer 112. The width of the stripscorresponds with a desired size of the magnetic domains. For instance,if the desired width of the magnetic domains is 1 micron, then the widthof the strips may be 1.2 microns. Because the magnetic domains are ableto spread along the length of the strips in data storage layer 112(which is up and down in FIG. 19), the next data storage layer in thestack of magnetic memory 100, which is data storage layer 122, may alsobe patterned into strips that are orthogonal to the strips of datastorage layer 112.

FIG. 20 illustrates data storage layer 122 as patterned in an exemplaryembodiment of the invention. Data storage layer 122 is also patternedinto strips similar to data storage layer 112. However, the strips ofdata storage layer 122 are orthogonal to the strips in data storagelayer 112. The magnetic domains are able to spread along the length ofthe strip (which is left to right in FIG. 20), but the magnetic domainsare controlled in those directions by the previous orthogonal strips. Bymaking the strips of the subsequent data storage layer orthogonal to theprevious data storage layer, the spread of the magnetic domains can becontrolled in all directions. If data storage layer 132 in FIG. 1 ispatterned into strips, then the strips would again be orthogonal to thestrips in data storage layer 122.

Data storage layers may be patterned into different shapes other thanstrips. For instance, a data storage layer may be patterned into domain“islands”, which is a section of material having a size of a desiredmagnetic domain. FIG. 21 illustrates data storage layer 112 as patternedin another exemplary embodiment of the invention. Data storage layer 112is patterned into domain-sized islands in this embodiment. The locationsof the islands correspond with the magnetic domains in data storagelayer 112. The area of the islands corresponds with a desired size ofthe magnetic domains. The next data storage layer in the stack ofmagnetic memory 100, which is data storage layer 122, may also bepatterned into similar islands.

FIG. 22 is a flow chart illustrating a method 2200 of fabricating amagnetic memory in an exemplary embodiment of the invention. Method 2200may be used to fabricate magnetic memory 100 illustrated in the previousfigures. Step 2202 comprises forming a plurality of read elements and aplurality of write elements. The read element may be formed in a firstlayer and the write elements may be formed in one or more other layers.For instance, the read elements may comprise an array of Hall Effectelements, spin valve elements, or tunnel valve elements. The writeelements may comprise a plurality of current loops that correspond withthe read elements. Step 2204 comprises forming a first storage stackproximate to the plurality of read elements and the plurality of writeelements. The first storage stack includes a first data storage layerdefining a first plane. Step 2206 comprises forming a plurality ofsecondary storage stacks proximate to the first storage stack. Thesecondary storage stacks each include a second data storage layerdefining secondary planes that are parallel to the first plane.

FIG. 23 is a flow chart illustrating a method 2300 of fabricating astorage stack, such as storage stack 110 in FIG. 1, in an exemplaryembodiment of the invention. Step 2302 comprises forming a heating layer116. Step 2304 comprises forming a data storage layer 112 proximate toheating layer 116. Step 2306 comprises forming an insulating layer 114proximate to data storage layer 112.

FIG. 24 is a flow chart illustrating a method 2400 of fabricating a datastorage layer in an exemplary embodiment of the invention. Method 2400will be described with reference to FIG. 2. Step 2402 comprises forminga first ferromagnetic layer 202. As stated in other embodiments,ferromagnetic layer 202 may comprise a multi-layer structure such asshown in FIG. 6. Step 2404 comprises forming an antiparallel (AP)coupling layer 204. Step 2406 comprises forming a second ferromagneticlayer 206. Ferromagnetic layer 206 may comprise a multi-layer structuresuch as shown in FIG. 6. Step 2408 comprises forming a thirdferromagnetic layer 208. Ferromagnetic layer 208 may comprise amulti-layer structure such as shown in FIG. 6. The data storage layerformed according to method 2400 has the characteristics defined inprevious embodiments of transitioning from an antiparallel couplingstate at ambient temperatures to a parallel coupling state at atransition temperature.

Although specific embodiments were described herein, the scope of theinvention is not limited to those specific embodiments. The scope of theinvention is defined by the following claims and any equivalentsthereof.

1. A magnetic memory, comprising: a first storage stack including afirst data storage layer defining a first plane; a plurality ofsecondary storage stacks fabricated on the first storage stack, whereinthe secondary storage stacks include second data storage layers definingsecondary planes that are parallel to the first plane; wherein the firstdata storage layer and the second data storage layers are each formedfrom a multi-layer structure exhibiting an antiparallel coupling stateat ambient temperatures.
 2. The magnetic memory of claim 1 wherein themulti-layer structure further exhibits a transition from theantiparallel coupling state to a parallel coupling state at a transitiontemperature that is higher than the ambient temperatures.
 3. Themagnetic memory of claim 2 wherein the multi-layer structure furtherexhibits a transition from the antiparallel coupling state to areceiving state at a receiving temperature that is higher than theambient temperatures and the transition temperature, wherein thereceiving state represents a drop in coercivity of the multi-layerstructure below a write threshold.
 4. The magnetic memory of claim 1wherein the multi-layer structure comprises: a first ferromagneticlayer; an antiparallel coupling layer formed on the first ferromagneticlayer; a second ferromagnetic layer formed on the antiparallel couplinglayer; and a third ferromagnetic layer formed on the secondferromagnetic layer; wherein the first ferromagnetic layer isantiparallel coupled to the second ferromagnetic layer and the thirdferromagnetic layer at the ambient temperatures; wherein the firstferromagnetic layer is parallel coupled to the third ferromagnetic layerat a transition temperature that is higher than the ambienttemperatures.
 5. The magnetic memory of claim 4 wherein the firstferromagnetic layer and the third ferromagnetic layer have a Curietemperature that is higher than the Curie temperature of the secondferromagnetic layer.
 6. The magnetic memory of claim 4 wherein the firstferromagnetic layer and the third ferromagnetic layer each comprisemultilayer structures comprised of alternating layers of Co and Pd orPt.
 7. The magnetic memory of claim 4 wherein: the second ferromagneticlayer comprises a multilayer structure comprised of alternating layersof CoNi and Pd or Pt; and the antiparallel coupling layer is comprisedof Ru or Ir.
 8. A method of fabricating a magnetic memory, the methodcomprising: forming a first storage stack that includes a first datastorage layer defining a first plane; and forming a plurality ofsecondary storage stacks on the first storage stack, wherein thesecondary storage stacks include second data storage layers definingsecondary planes that are parallel to the first plane; wherein the firstdata storage layer and the second data storage layers are each formedfrom a multi-layer structure exhibiting an antiparallel coupling stateat ambient temperatures.
 9. The method of claim 8 wherein themulti-layer structure further exhibits a transition from theantiparallel coupling state to a parallel coupling state at a transitiontemperature that is higher than the ambient temperatures.
 10. The methodof claim 9 wherein the multi-layer structure further exhibits atransition from the antiparallel coupling state to a receiving state ata receiving temperature that is higher than the ambient temperatures andthe transition temperature, wherein the receiving state represents adrop in coercivity of the multi-layer structure below a write threshold.11. The method of claim 10 wherein: forming a first storage stackcomprises forming a first heating layer, forming the first data storagelayer, and forming a first insulating layer; and forming a plurality ofsecondary storage stacks comprises forming a second heating layer,forming the second data storage layer, and forming a second insulatinglayer.
 12. The method of claim 8 wherein forming the multi-layerstructure of the first data storage layer or the second data storagelayer comprises: forming a first ferromagnetic layer; forming anantiparallel coupling layer on the first ferromagnetic layer; forming asecond ferromagnetic layer on the antiparallel coupling layer; andforming a third ferromagnetic layer on the second ferromagnetic layer;wherein the first ferromagnetic layer is antiparallel coupled to thesecond ferromagnetic layer and the third ferromagnetic layer at theambient temperatures; wherein the first ferromagnetic layer is parallelcoupled to the third ferromagnetic layer at a transition temperaturethat is higher than the ambient temperatures.
 13. The method of claim 12wherein the first ferromagnetic layer and the third ferromagnetic layerhave a Curie temperature that is higher than the second ferromagneticlayer.
 14. The method of claim 12 wherein: forming the firstferromagnetic layer comprises forming alternating layers of Co and Pd orPt; and forming the third ferromagnetic layer comprises formingalternating layers of Co and Pd or Pt.
 15. The method of claim 14wherein: forming the second ferromagnetic layer comprises formingalternating layers of CoNi and Pd or Pt; and forming the antiparallelcoupling layer comprises forming a layer of Ru or Ir.
 16. A magneticmemory, comprising: a first storage stack including a first data storagelayer defining a first plane, wherein the first data storage layer isformed from a multi-layer structure exhibiting an antiparallel couplingstate at ambient temperatures; a second storage stack proximate to thefirst storage stack, wherein the second storage stack includes a seconddata storage layer defining a second plane that is parallel to the firstplane, and wherein the second data storage layer is formed from amulti-layer structure exhibiting an antiparallel coupling state at theambient temperatures; and a third storage stack proximate to the secondstorage stack, wherein the third storage stack includes a third datastorage layer defining a third plane that is parallel to the first planeand the second plane, and wherein the third data storage layer is formedfrom a multi-layer structure exhibiting an antiparallel coupling stateat the ambient temperatures.
 17. The magnetic memory of claim 16 furthercomprising: a control system adapted to heat the first data storagelayer to transition the first data storage layer from the antiparallelcoupling state to a receiving state where the coercivity of the firstdata storage layer drops below a write threshold; and a plurality ofwrite elements proximate to the first data storage layer, wherein thewrite elements are adapted to apply magnetic fields to the first datastorage layer to create a plurality of magnetic domains in the firstdata storage layer representing a plurality of bits; wherein the controlsystem is further adapted to cool the first data storage layer totransition the first data storage layer from the receiving state to theantiparallel coupling state to store the magnetic domains in the firstdata storage layer.
 18. The magnetic memory of claim 17 wherein: thecontrol system is further adapted to heat the second data storage layerto transition the second data storage layer from the antiparallelcoupling state to a receiving state where the coercivity of the seconddata storage layer drops below a write threshold; the control system isfurther adapted to heat the first data storage layer to transition thefirst data storage layer from the antiparallel coupling state to aparallel coupling state where the magnetic domains representing thestored data are emitted as external stray fields that imprint themagnetic domains in the second data storage layer; the control system isfurther adapted to cool the second data storage layer to transition thesecond data storage layer from the receiving state to the antiparallelcoupling state; and the control system is further adapted to cool thefirst data storage layer to transition the first data storage layer fromthe parallel coupling state to the antiparallel coupling state.
 19. Themagnetic memory of claim 18 wherein: the control system is furtheradapted to heat the third data storage layer to transition the thirddata storage layer from the antiparallel coupling state to a receivingstate where the coercivity of the third data storage layer drops below awrite threshold; the control system is further adapted to heat thesecond data storage layer to transition the second data storage layerfrom the antiparallel coupling to a parallel coupling state where themagnetic domains representing the stored data are emitted as externalstray fields that imprint the magnetic domains in the third data storagelayer; the control system is further adapted to cool the third datastorage layer to transition the third data storage layer from thereceiving state to the antiparallel coupling state; and the controlsystem is further adapted to cool the second data storage layer totransition the second data storage layer from the parallel couplingstate to the antiparallel coupling state.
 20. The magnetic memory ofclaim 16 wherein the multi-layer structure of the first data storagelayer includes: a first ferromagnetic layer; an antiparallel couplinglayer formed on the first ferromagnetic layer; a second ferromagneticlayer formed on the antiparallel coupling layer; and a thirdferromagnetic layer formed on the second ferromagnetic layer; whereinthe first ferromagnetic layer and the third ferromagnetic layer of themulti-layer structure have a Curie temperature that is higher than theCurie temperature of the second ferromagnetic layer.
 21. The magneticmemory of claim 20 wherein: the control system is adapted to heat thesecond ferromagnetic layer of the first data storage layer above itsCurie temperature with the first ferromagnetic layer and the thirdferromagnetic layer below their Curie temperatures to transition thefirst data storage layer from the antiparallel coupling state to aparallel coupling state.
 22. A method of writing to a magnetic memorycomprising a plurality of storage stacks, wherein each storage stackincludes a data storage layer formed from a multi-layer structureexhibiting an antiparallel coupling state at ambient temperatures, themethod comprising: heating a first data storage layer of a first storagestack to transition the first data storage layer from the antiparallelcoupling state to a parallel coupling state; applying magnetic fields tothe first data storage layer from write elements that are proximate tothe first data storage layer to create a plurality of magnetic domainsin the first data storage layer representing a plurality of bits; andcooling the first data storage layer to transition the first datastorage layer from the parallel coupling state to the antiparallelcoupling state to store the magnetic domains in the first data storagelayer.
 23. The method of claim 22 further comprising: heating a seconddata storage layer of a second storage stack that is proximate to thefirst storage stack to transition the second data storage layer from theantiparallel coupling state to a receiving state where the coercivity ofthe second data storage layer drops below a write threshold; heating thefirst data storage layer to transition the first data storage layer fromthe antiparallel coupling state to a parallel coupling state where themagnetic domains representing the stored data are emitted as externalstray fields that imprint the magnetic domains in the second datastorage layer; cooling the second data storage layer to transition thesecond data storage layer from the receiving state to the antiparallelcoupling state; and cooling the first data storage layer to transitionthe first data storage layer from the parallel coupling state to theantiparallel coupling state.
 24. The magnetic memory of claim 23wherein: heating a third data storage layer of a third storage stackthat is proximate to the second storage stack to transition the thirddata storage layer from the antiparallel coupling state to a receivingstate where the coercivity of the third data storage layer drops below awrite threshold; heating the second data storage layer to transition thesecond data storage layer from the antiparallel coupling state to aparallel coupling state where the magnetic domains representing thestored data are emitted as external stray fields that imprint themagnetic domains in the third data storage layer; cooling the third datastorage layer to transition the third data storage layer from thereceiving state to the antiparallel coupling state; and cooling thesecond data storage layer to transition the second data storage layerfrom the parallel coupling state to the antiparallel coupling state.